'Superbugs' resistant to antibiotics could be strengthened by pollution

• As we inch closer to a post-antibiotic era, a study finds that pollution could be contributing to antibiotic resistance
• Heavy metal contamination stimulates antibiotic resistance genes in soil bacteria
• This type of pollution also increases bacterial diversity

When you go on a round of antibiotics, you're always warned about antibiotic resistance if you don't finish your course. 

The invention of antibiotics was a game-changer in healthcare. Finally, we could survive many infections that before would have been death sentences. But for a while now, scientists in the medical community have warned of a post-antibiotic era, as a result of our heavy reliance on these drugs. 

More bacteria are becoming resistant to antibiotics due to overprescription and patients not finishing their courses, and there have been many efforts worldwide to better manage our antibiotic use.

But, a new study has found signs that pollution could also be helping to create these superbugs. 

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Evidence in the soil

A study published in Microbial Biotechnology, analysed the soil around South Carolina's Savannah River, looking at heavy metal and radioactive contaminants and how they affect bacteria in the ground.

"Previous studies have demonstrated that heavy metal contamination in the natural environment can play an important role in the maintenance and proliferation of antibiotic resistance," write the researchers.

"This co-selection phenomenon is the result of antibiotic and metal resistance phenotypes sharing many overlapping genetic mechanisms, including co-resistance (close linkage between multiple different resistance genes), cross-resistance (single genetic elements that regulate both antibiotic and metal resistance genes) and co-regulation (shared regulatory system with antibiotic and metal resistance)."

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Heavy metal contamination

The industrial age, alongside agriculture, has introduced various heavy metals into the natural environment that end up in water sources, the ground, air and even animals. It became important to the researchers to also understand how this could impact on bacterial communities.

They chose the Savannah River site for their research because of its historical association with the nuclear industry as it has been exposed to nuclear materials manufacturing, coal-fuelled power plants, nuclear reactors, waste management and other research.

Over the decades, there have been many leaks and improper disposal of waste, which means the riverbanks are, ideally for this study, polluted with heavy metals and radioactive atoms. They compared the bacterial communities from pristine areas to those of the more polluted areas.

They sequenced the rRNA genes of the microbial communities and found that elevated heavy metal contamination can promote antibiotic and biocide resistance in bacteria. By becoming more resistant to heavy metals, they also become more resistant to antibiotics.

Most of the metal-resistance genes found were associated with copper, arsenic, iron, nickel, zinc, molybdenum resistance. Heavy metal exposure also creates more bacterial diversity in the sample sites.

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Vancomycin

They also had some interesting results in the case of vacomycin, an antibiotic that's normally used in the worst-case scenario and is rarely used in hospitals.

Resistance to this particular antibiotic has been found in bacterial genes in various environments like the ocean, human excrement and even 30 000-year-old permafrost, and the researchers theorise in their study that these genes in the soil could enhance the survival and fitness of bacteria.

However, they would need to conduct more tests to confirm this.

Fighting antibiotic resistance

This research is important to create a better understanding of antibiotic resistance, especially as we face an oncoming health crisis in the near future.

"We found that certain bacterial taxa are differentially affected by edaphic factors and heavy metal contamination and that their presence can have an important role in the dissemination and maintenance of antimicrobial and metal resistance."

"Even in areas with low levels of heavy metals, antibiotic and heavy metal resistance can be both ubiquitous and widespread."

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